Electrical control system



May 31, 1949.

Filed Nov. 23, 1945 SOURCE OF DVC- ELECTRICAL CONTROL SYSTEM 2 Sheets-Sheet 1 INVENTUR Edwin MCauender.

ATTORNEY y 1949- E. M. CALLENDER 2,472,043

ELECTRICAL common SYSTEM Filed Nov. 2:, 1945 2 Sheets-She et 2 "we; in

ATTORNEY Patented Meyill, 1949 2 UNITED STATES PATENT OFFICE ELECTRICAL CONTROL SYSTEM Edwin M. Callender, Cynwyd, Pa., assignor to The Budd Company, Philadelphia, Pa., a corporation of Pennsylvania Application November 23, 1945, Serial No. 630,401

' 18 Claims. 1

. This invention relates to electrical control systems and more particularly to systems which are dependent upon load change primarily for introducing a control sequence.

In the conventional electrical system where power is applied to a load it is common practice to employ, where a series loads is involved, a

timing mechanism during which power is applied to the load. In the use of the timer, indicating nevertheless the indication of timer completion will occur, and ii the load is removed it would be insufllciently treated. This arises from the fact that the timing is an arbitrary step in the method of treatment and is not related to the state of the load as indicating the normal completion of the treatment. Such considerations apply to a variety of material, manufacture and treatment, such as heating methods; welding methods, and the like.

Particularly in welding operations from the viewpoint of electrical efliciency, economy and time saving, it is of considerable importance that the time of power application be related to the period in which the weld actually takes place. Difiiculties in accomplishment of this result are abundant, such as electrode pressure variations, chance current changes, variations in electrode contour, variations in contact resistance at the electrodes, and other factors.

Generally stated, an outstanding object of the present invention is to provide an improved electrical control system which functions on a change in the load condition indicating completion of the treatment. Another object of the invention is the provision of a control system in which improved current compensating means are employed to overcome changes in the voltage which are not related to the change of condition of the load itself. Still another object of the invention is to provide an improved form of circuit functioning as a comparator whereby an initial voltage comparable to the pre-change load voltage is established in a circuit and the diversion of the voltage from this pre-change voltage is registered in the apparatus and utilized as an operating means to bring about an indication of completion of load treatment, a disconnection of the power source from the load, or any unrelated power actuation. A further object of the invention is to provide an improved form of load treatment completion indication utilizing both visual and graphic means. Additional objects are to provide measuring means for the diilerential between the fixed time and the actual time of load treatment; to provide a bridge circuit permitting use of vacuum electronic tubes; to provide control means for changing but not cancelling current flow in the power source; and to increase the normal speed of action of the circuit as described. Other objects of the invention will appear on further consideration of the specific details of the invention as applied to a form of the invention which may be preferred and hereinafter described and illustrated in the accompanying drawings, in which:

Figure l is a diagrammatic view of the electrical circuits and apparatus employed to accomplish the objects of the invention;

Figure 2 is a wiring diagram of the circuit applicable to the visual and graphic indicating means;

Figure 3 is a wiring diagram illustrative of a use of the invention modified from that of Figure 1; and

Figure 4 is a detail indicative of the graphic mechanism employed to indicate the completion of the load treatment.

The control system of this invention in its broadest conception is applicable in any circuit in which a load receives power from an electrical source either in one amount or shot or in a plurality of amounts or shots in sequence. It is, of course, also applicable to the supply of power to a series of loads in a continuous sequential treatment from a power source irrespective of the nature of the power. However, in order to make clear the usefulness of the development as associated with a specific type of load, the drawings of the application and the specific description both relate to an adaptation of the system to a resistance spot welding circuit wherein power is supplied in a series of continuing shots, each for a brief interval of time. To this end the circuit as illustrated may be divided into four sections: A, the power section including the welding transformer and the electrodes; B, the power control section; C, the weld controlled section; and, D (Fig. 2) the indicator section.

Taking up the mentioned sections of the circuit of Figure 1 as indicated above, section A, or the power section, includes a welding transformer l including a primary coil 2 and secondary coil attracts 3 suitable for supplying the heavy currents necessary for welding purposes. The secondary 3 has direct connection to the electrodes 4 and 5 which are adapted to receive a workpiece, such as 6 in the form as illustrated, of two overlapping metal sheets disposed between the electrodes for welding. Power is supplied the primary 2 of the welding transformer from a source of alternating current indicated by the numeral I, this power being directly controlled by a contactor 8 in the B section interposed in the transformer wiring with the primary coil terminals in series therewith. The contactor 8 takes the usual form now conventionally in use of inversely connected ignitrons 9, I adapted to transmit alternate half cycles ofcurrent from the source to the primary. These ignitrons are supplied with igniters II adapted for energization by the timing circuit formed of branches, generally indicated by the numerals l2, I3 and I4. This is a direct current circuit which includes a trigger tube I in branch I2, an auxiliary control tube I6 in branch I3, and direct thyratron control tubes I! in branch I4. By means of the variable resistor I8 in branch E2 the number of cycles in which welding current is supplied to the workpiece is fixed so that by adjusting the value of this resistance the time period of current application to the load is properly controlled.

In addition to the time control this circuit also employs a heat control indicated generally by the numeral l9. This heat control, as shown, is in the form of a phase shift wherein by appropriate variation of a resistor in the phase shift bridge the fraction of each half cycle of current which is applicable to the load circuit is determined. Voltage compensating means 2| is also indicated in parallel with the heat control branch circuit I9.

Various timing, heat and voltage controls as related to the power unit A are used conventionally by manufacturers of welding equipment and specifically do not enter into the invention. The operation of .these controls appears in numerous publications, such as Electronic Control of Re sistance Welding by George M. Chute, McGraw- Hill Publishing Company, and therefore will not be described in detail here. Mention should be made, however, of the following items in connection with this control circuit. Resistor I8 in branch I2 which controls the timing obviously is made inefiective by short-circuiting of the same as indicated by a conductor so that by application of the short-circuiting conductor 25 the time of power application is reduced to a small amount. The voltage drop applicable to control tube I6 by means of which the power timing is attained may be nullified by opposing voltage drop applied across a resistor 26 in the branch circuit I3 by means of conductor TI whereby the timing action of the control is made ineffective and the power supply cut off. The heat supply as controlled by the phase shift circuit I 9 may be til reduced to a small amount by short-circuiting a substantial section of the phase shift bridge resistor 20 through conductors 28 and 29. Conductor 30 in timing control branch I2 may be opened at will to deenergize the timing circuit. Each of these alternative deenergizing means may be employed by insertion in each of the conductors mentioned of relay switches, normally closed relay switch RI-I being in series with conductor 30, normally open switch RI-2 being in series with conductor 25, normally open switch RI-3 being in series with'conductor 21, and normally open :3 switch RI-l being in series with conductors 28 and 25. Each of these relay switches is connected in fixed relation to a movable core operable by the relay coil Ri, as 1s also another normally open switch RI-5 later to be described. Selection of the appropriate deenergizing means is made by the short-circuiting manual switches 31 in each of the conductor circuits mentioned.

Mention should be made also of the initiating switch circuit 40 including the relay coil R2 effective on energization by closure of initiating switch 42 to close relay switch R2--I adjacent the timing circuit section I2. Switch 42 may be either manual or, as is usually the case, automatic in the sense that a sequence circuit is effective to close and open the switch at recurrent. uniform intervals.

The circuits A and B as above described relate to a specific type of load and power control means appropriate for this load, as in a welding system. Description will now be given of control means in section C dependent upon the state of the load to bring about a power manifestation in the same or a separate circuit either to indicate a completion of load application visually or graphically or by actual interruption of the supply of power from the source of the load. Section C may be readily divided into rectifier, current compensating, comparator, percentage control and power units.

At points, preferably closely adjacent the electrode tips of the power circuit as described and illustrated in my copending application Serial No. 533,977, new Patent #2433327, January 6, 1948, filed May 3, 1944, conductor taps are made leading to the amplifying and rectifying circuit including the transformer 5|, the rectifying tube 52, and the filter circuit with the capacitors 54 and the choke coil 55. Tool inductive effects are neutralized by a variable inductor 49 adjacent the welding yoke circuit.

In addition, means are provided for lifting the level of the filtered voltage to overcome lag in arriving at the peak electrode voltage. As shown, the two filter conductors beyond the rectifier 52 and between the choke coil and transformer are connected through a rectifier I95 to the secondary of a transformer I96; The alternating current source I91 supplies power to the transformer I96 through variable resistor I99 and also to tube filament transformer 198.

The outlet points 56 and 51 are connected to a current compensating branch circuit, a resistance 53 being connected between the outlet points to slow down the discharge of the capacitors 54. This circuit includes a current transformer 58, forming part of the welding circuit secondary, an amplifying transformer 59, a. bridge rectifier 60 between a tapped section of the secondary at point I90, and connections to the positive fixed point GI and the potentiometer 62 establishing the negative terminal of the rectified circuit at point 48. Two vacuum tubes 63 and 64, 63 being a triode amplifier and 64 a pentode amplifier, are connected between points 6| and 48 of the current compensating circuit, and points 56 and 51 of the rectified weld-connected circuit as follows: 48 is connected to the cathode 65 and to the supp essor grid 69 of tube 64, 6| is connected through an opposing potential such as the battery 66, and also through a resistor 61 to the control grid 68 of tube 64. Point 56 of circuit 50 is connected to the outlet point I1 and point 51 is connected to the anode 79 of tube 63. In addition, the cathode 'II of tube 63 is connected through a resistor I2 to the anode I3 of tube 64. The cathode II of tube 83 is connected to the screen grid I4 of tube 84. Control grid of tube 83 is also connected to the anode I3 of tube 84. It appears by these connections that points I6 and 11 are established as the outlet points of the connections to the electrodes 4 and 8 after current compensation. A fixed voltage from a source of direct current I8 is applied across tube 64 to insure functioning within the linear characteristic of the Eg-Ip curve.

The operation of the section of the C unit as hereinabove described follows: On receiving an alternating current impulse between the electrodes 4 and 5, the branch circuit 50 amplifies and rectifles the same and passes it into the compensating circuit at the tubes 53 and 84. Since the rectified potential from transformer I88 is derived from a constant independent source, the filter system is loaded by being charged to an elevated voltage and consequently the signal energy necessary to start the circuit sequence is greatly reduced. For example, if the operating peak be 350 volts and the operating range 300 to 350 volts, a maintenance of voltage at 275 volts eliminates the time for charging from zero to 275 volts. Thus the circuit responds properly to a short weld of one or two cycles as readily as to one of five or six cycles. If there is no variation in the secondary current, there will be no modification in this transmission, and the outlet points I8 and II will constitute points of uniform potential difference with the point I8 positive in relation to the point 11. During this condition the current transformer 58 transmits a voltage which is amplified and applied at points BI and 48 as a constant potential difference, with the point 6| being positive in relation to 48. The value of the voltages at 8i and that due to the battery 88 are preferably selected so that possible voltage changes due to. current variation come within the range of the selected voltages. In any event, the opposition of the voltages will reduce the voltage difference between the cathode 65 and control grid 58 of tube 64, permitting an increased flow of current through this tube. Should a variation of the current occur in the welding secondary, as, for example, a decrease in current, the result will be the development of an increased voltage at the cathode 65 due to the lessening of the opposing voltage BI, 48 as against the voltage of battery 86. Consequently, relative to the cathode, the bias voltage of control grid 88 reduces in value thereby decreasing the effective resistance of tube 84 to current passing therethrough from constant source I8 and thus causing a decrease in the negative bias of grid IS in tube 83 and an increase of voltage as between points it and TI. the outlet points of the weld control circuit 50. In this manner compensation is made for current variation in the welding secondary circuit.

The third unit of the C section may be termed a comparator inasmuch as it establishes an initial voltage impressed thereon as a basis of comparison with a subsequent voltage of the circuit and through this difference of voltages the control or indicating sections of the circuit are energized.

The comparator unit includes a capacitor II, which may be referred to as the memory circuit capacitor, connected to the positive point 82 of conductor 91 and through a rectifying tube I00 and variable resistor 80 to the point 8|, points 82 and BI corresponding to outlet points I6 and II respectively of the C section unit. Thus the ca- 6 voltage occurring between points 8| and 82, which in turn are components of the load voltage. By adjusting the contact arm 83 of potentiometer 80, which may be referred to as the percentage resistor, and which is connected directly across points 8| and 82, the capacitor IOI may be charged to any desired percentage value of the load voltage component since the resistance of potentiometer 80 is uniform along the length.

Since the tube I00 transmits current in one direction only, there is no discharge of the capaciby the relay coil R2 of the initiating circuit 40 when the welding power is applied to the main circuit. It is the function of the control apparatus to translate the comparator voltage values as determined by the potentiometer 80 into percentage values of the voltage effective at the weld. This is accomplished by connecting to the percentage resistor, operating circuits which function on a change of potential from that initially established by the comparator to another potential equal to the percentage value which the points 8|, 82 of the electrode potential may assume.

In order to effectuate this voltage change, use is made of a comparator bridge arrangement including the vacuum tubes 84 and 85 and the equal resistors 88 and 81 forming the four branches of the bridge. A relatively constant current supply is obtained from the source 88, the positive potential being applied between the resistors 88 and 8'! and the negative potential being applied to the bridge through the contact 88 of a variable resistor 90. The function of the resistor 80 is to permit the bridge to be set with an initial negative bias from zero for the condition prior to application of the incoming voltage BI, 82. The purpose of this construction will appear in the following description.

Tubes 84, 85 of the bridge are of the same type, but when the potential of an incoming signal impulse is applied at points BI and 82 the grids of the same are subject to different voltages. The grid 8| of tube 84 is connected to a voltage dividing circuit between points 8i and 82 including resistors 82 and 83 so that the point of con nection 88 is substantially below in voltage that of point 82. The grid 85 of tube 85 is connected to the comparator unit at a point 86 in a circuit including the conductor. 81 and resistors 88 and 88, the ratio of the resistance of resistor 88 to resistor 88 being the same as that of resistor 83 to resistor 82. these circuits are such preferably that the voltage of grids 9| and 85 are equal when the arm 83 of the percentage potentiometer is at its upper or maximum voltage point. Consequently, un-

der normal operation for a given percentage setting of the potentiometer 80, the efiective resistance of tube is less than that of tube 84 because the negative potential on grid 85 of tube 85 is less than that on grid 9i of tube 88. Since the resistances 88 and 81 of the bridge are the same, point I08 is maintained negative relative to point I05, thus unbalancing the bridge to maintain a power tube I08 inoperative. The potential at point I05 is applied to the cathode and one grid of tube I08 and the potential at point I08 is applied to another grid of the tube and the tube characteristics are such that it will fire pacitor is charged in proportion to the maximum 75 when the bias of the tube grids reaches a pre- Accordingly, the resistances of arran e determined relationship, as when the potent at I and I08 are equal. with this condition of unbalance existing at the inception of the incoming signal, when the voltage drop on fusion at the weld occurs, the potential of grid 8| approaches the potential of grid 95 which is being maintained by the capacitor IOI at the peak voltage value, until at the point of approximate potential equality the bridge becomes balanced, the potential of point I06 becoming equal to or positive in relation to point I05, and the tube IOI strikes. Thus the cut-out or other power or indicating mechanism is energized.

The shift in balance of the bridge 84, 85, 86, 8] brought about by a change in potential at points 8|, 82 is effective at bridge points I05 and I06. Prior to the change of potential the bridge balance is such that the cathode I0'l of the gas tetrode I08 is, in relation to the control grid I08, at a value preventing energization of the tube. Assuming that the tube will strike and develop a current flow between the anode I I0 and cathode I01 when the bridge is at or above zero balance in the positive sense, then the necessity of the unbalancing resistor 90 appears since by use of this resistor the actuation of tube I08 from the chance voltage variations is prevented. Since the shift of voltage due to the potential change atpoints 8 I, 82 is substantial, amounting to as much as 90 volts, it is apparent that the initial unbalancing of the bridge, as between 0.5 to 2.0 volts,

by- -resistor 90 does not hinder the efiectiveness of the bridge operation. Accordingly, when a voltage change occurs at 8|, 82 the bridge is unbalanced in the positive sense reducing the negative bias of grid I09 and causing the tube I08 to strike thereby to energize coil RI of the relay switch unit and bring about actuation of any one of the four circuit-modifying means hereinabove described. Power applicable to tube I08 and the series-connected coil RI is derived from the constant potential source II I. The circuit of tube i08 includes also, in addition to relay coil RI, the time delay relay coil R3, a variable resistor l I3, and a Contact switch R23 operated by relay R2. A variable resistor H5 is connected in shunt with the time delay relay coil R8 to vary the time of relay energization in accordance with the tolerance desired. Also, conductor '2'! of branch circuit E3 of the power control circuit B is connected in parallel with the tube and resistor H3, this circuit including the normally open relay switch Ri3 and the manual switch 37.

There is shown also in the circuit, cathode ray tuning indicators, as indicated by the numerals I20 and IZI. The purpose of the indicator I20 is to establish an indication that the proper signal is supplied from the welding tool and also that a correct proportion of the developed voltage may be fed into the current compensator. To this end the tube I20 is connected across the constant potential source 88, and its grid I22 is connectible through the switch ISI to the slide arm I23 of the potentiometer I24. The potentiometer is connected across points BI and 82 through a resistor I I9. By adjustment of the potentiometer I24 the point indicating a proper signal at thetool may be secured as a preliminary adjustment. Also, the grid I22 is connectible by means of switch I9I, potentiometer 'I92, and conductor I93 to the point I90 of the current compensator transformer secondary. This point is connected to a potentiometer slider arm I32a so that voltage variation as desired may be secured and made has connection to the potentiometer I28 for this purpose. While helpful in facilitating adjustment, these cathode ray tuning indicators are not essential to the operation of the system.

In Figure 2 of the drawing there is illustrated a circuit which is used in connection with visual and graphic indicating means. This circuit consists primarily of three lamps I30, I3I and I32; having in parallel therewith respectively electromagnets I33, I34 and I35. Lamp I30 is green in light transmission, lamp I3I transmits an amber light, and I32 a red light. This indicating circuit is so adjusted that the amber light I3I is ener gized when the power is applied to the load, this light indicating initial supply of energy into the weld and being succeeded by the green light I30 when the load through a voltage change in the same brings about a voltage change in operation of the load-control circuit. The green light is maintained until the normal time period ends as set by the timer or the initiating switch 42 opens, unless this time period is in excess of the time necessary for actuation of time delay coil R3 in the circuit of tube I08. If the latter condition be the case, then the green light goes out and red light I32 becomes lighted, thus indicating that the set time of closure of the power circuit is in excess of the time required for securing a com- 35 plete application of power to the load. It also indicates the presence of excessive energy in the weld, if the percentage dial has been correctly set. If this lighting sequence with the appearance of the red light continues, then adjustment may be made so that the time or amount of power application may be reduced.

In order to make clear the operation of the indicator circuit of Figure 2, it is pointed out that the relay switches R2-4, R2-5 are closed coincident with the closure of initiating switch through functioning of the relay coil R2. On closure of relay switch R2-4 a circuit is immediately established through the amber light I3I and also through relay coil R0, whereby relay switch R4I locks in the coil to maintain light in lamp I3I, alternating current power being supplied from source 200 and relay switch R2-6 being closed by initiating coil R2. comes effective in the load and a change of voltage occurs therein suthcient to bring about the functioning of the load-control coil RI, this coil becomes operative to close relay contact switch RI-5 as well as the switches hereinbefore mentioned operative to interrupt the circuit of the power supply to the load. On closure of switch RI-5 green lamp I30 becomes lighted and at the same time relay coil R5 operates to lock in green lamp switch R5l and to open normally closed relay switch R52 in the amber light circuit. This condition maintains until the time delay relay R3 develops suflicient energy to close normally open relay switch R3--I, thereby lighting the red lamp I32 and energizing relay coil R6 to lock in switch RB-I and to open normally closed switch R62 in the green lamp circuit and the normally closed switch R63 in the amber light circuit. It is apparent that the red lamp will not become lighted if switches R2-4 and R25 are opened due to end As soon as the power beof timer period or opening of switch 42 in the initiating circuit. a

The electromagnets I33, I34 and I35 being connected in shunt with the lamps are of course energized coincidentally therewith. In order to secure a graphic record of control periods, in the present arrangement this Is accomplished by means of these electromagnets in connection with movable armatures, inking pens, and a traveling p per roll. Reference is made to Figure 4 of the drawing for a diagrammatic showing of apparatus which is associated with the electromagnets I33, I35 and I35 to secure this record. As indicated. the armatures I 68, I49 and I56 carry terminal pen points II, I52 and I53 at one end and are pivoted in alignment at the other end. The pen points are adapted to engage paper ltd wrapped about a roll rotatable on the shaft I55 in the direction indicated. Suitable mechanism for controlling th movement of the drum, in-

eluding power units and connections for rotation of the drum during the application of power to the load, is provided.

The operation of sections of the circuit has been indicated hereinabove, but it may be helpful o consider briefly the sequence of operation of the unit as a whole and as applied to resistance welding. Before starting the welding operation, the voltage sources including 1, 66, I8, 88, Ill, It? and the control source of direct current in the B section are applied to the circuit and the percentage resistor 86 and unbalancing resistor 99 adjusted by aid of the cathode ray indicators I and I2I. Assuming the interposition of a workpiece or load as designated by the metal sheets 6 between the electrodes I and 5, power is applied for welding purposes by closure of switch 42 in the initiating circuit, this closure being either manual or automatic in the case of a sequence-operated system. Energization of relay coil R2 results in closure of switches in the indicating circuit as mentioned and also closure of normally open relay switch R2-3 in the power circuit of tube I68, relay switch RZ-S in the indicator circuit of Figure 2, and the relay switch R2I in the power control circuit thereby caus- Ing functioning of the timing circuit and the related heating and voltage control circuits, and resulting in the application of the welding current to the workpiece. The resistance of the workpiece is generally maintained until fusion occurs at the interface between the sheets, and in this time interval prior to fusion the comparator unit develops the initial maximum voltage ffective at the weld point through the instrumentality of the capacitor IIII. During this time interval, should there be a change in current, the compensator unit, 58, etc.. corrects for this change.

In this initial time interval and before fusion at the weld point the amber lamp of the indicator is also energized, showing to the operator that current is being applied.

When the workpiece fuses at the interface, a continuing decrease in resistance at the weld results as the nugget enlarges accompanied by a drop of potential which is transmitted by the C circuit and made effective across the percentage resistor. At the proper point of time this drop brings about a strong unbalance of the bridge circuit in the direction necessary for actuation of the associated power circuits, whereupon power tube I68 is energized and relay RI connected thereto is caused to function to operate its core to open switch RI-I of the power circuit and to close its other switches including Rl-5 to light the green lamp in the indicator panel, through R5 and R5I, as well as shutoff the amber lamp, through R52. This condition maintains until the time delay switch coil R3 in the load power circuit operates to close switch R3-I and through relay R6 and switch R6-I to light the red lamp and, by relay R5 and switches R52 and R63 cut off the green lamp, and to open a gap in the circuit of an amber lamp; or until the timer or initiating switch 52 opens.

The particular advantages of the circuit as described include the effective current compensation of the voltage as derived from the load. so that irrespective of fluctuations in current there is attained a voltage value which is dependent primarily only on voltage change at the load. Of outstanding importance in the circuit also as promoting practical operation of the same is the utilization of the bridge in association with the comparator wherein vacuum tubes are employed. In balancing operations it has been found that greater evenness and uinforrnity and accuracy of balance can be secured utilizing vacuum tubes as against tubes containing various atmospheres, and the described arrangement provides an effective circuit for use of vacuum tubes in this connection. The circuit also has outstanding merit in the facility in which not only disconnection of a power source may be made as applied to the load, but in also providin other indications of load treatment completion, either visual or graphic. of the scope of the circuit, which is not restricted to the cutting-out of a power source effective on the load of the same power source. Obviously the power circuit of the load-responsive means may be utilized for any other purpose, such as the making or breaking of a power circuit unre lated to the power source for the load of the circuit. Thus in its general scope the invention has to do with a control circuit which functions on a change of voltage current in the load and operates to actuate any associated power circuit either for indication or cut-out or for other functions.

While the description as made hereinabove has for purposes of illustration been applied to a welding circuit in which operation of the load control is dependent upon a drop of potential in the load circuit, obviously the load control may function on an increased voltage at the load point or at any other point comparable to the load point. In Figure 3 of the drawing I have indicated a circuit arrangement which may be applied to a load for operating a load control on increase of voltage at the load point. The points I66 and I6I correspond, to points 8! and 82 of Figure 1, with point I6I positive in relation to point I65. The percentage resistor is indicated by the numeral I62, but in this form of the disclosure the capacitor I63 is connected directly to the grid I64 of the vacuum tube I65 on the negative side of the circuit. Tube I65, in conjunction with vacuum tube I66 and associated resistors I51 and I68, form the branches of the bridge similarly as described in conjunction with Figure 1. Source I69 supplies power to the bridge at points I10 and III, the connection at I'll to the bridge being through variable resistors M2 to effect initial unbalance of the bridge. The grid I13 of tube I65 is connected through a resistor I" to the movable contact I15 of the percentage resistor I62. Also, the outlet terminals I16 and IT! of the bridge have connection to the cathode I18 and control grid I19, respectively. of gas power Observation should be made tube I60 so that when the proper relation between grid and cathode is established the tube strikes and permits the transfer of power from the positive source point I8I through the tube to the negative point I82 of the source. Thereupon the potential drop of the circuit is utilized at terminals I83 for any desired power function.

The operation in this form of the system is dependent upon an increase in voltage across the terminals I60 and I6I to bring about a shift in the bridge balance to that side of the zero point which will permit operation of the power tube I60 in the operating circuit. Initially the source voltage is impressed upon the grid I64 of tube I65 and the capacitor I63 through the time delay switch I94. The capacitor I63 is thus charged to the impressed voltage and after one or two cycles the time delay switch operates to open the circuit, the capacitor then maintaining the voltage on the grid I64, pending voltage variation in the incoming current. On an increase of voltage from the source effective on the grid I13 of tube I66, this tube is brought to the balance point in a manner similar to that described in the principal form of the invention.

As described, the circuit is usable for seam welding if the signal is taken off the rollers near the point of weld.

Various detail modifications of the described circuit may be made. For example, the resistors '66 and '99 in the voltage fixing circuit may be omitted and capacitors substituted.

Other modifications of the invention mayor course be made, the showing being diagrammatic and subject to rearrangement suitable for the desired loads and applications of the system. Hence no limitation is implied by the disclosure other than that which may be required by the claims as hereto appended.

What is claimed is:

1. In a system of power supply control including a power source and a load unit receiving power from said source and subject to voltage change, means for correcting the load voltage to compensate for current fluctuations, load'controlled circuital apparatus comprising a comparator connected to the load for fixing a reference voltage which is determined by a component of the maximum compensated load voltage prior to voltage change for comparison with a voltage which is determined by subsequent compensated load voltage values, percentage means for fixing the percentage of voltage change effective to actuate said apparatus, and power means effective on change of comparator voltage to the set percentage value to operate said apparatus.

2. In a system of power supply control including a power source and a load unit receiving power from said source and subject to voltage change, load controlled circuital apparatus comprising a comparator connected to the load for fixing a component of the load voltage prior to voltage change for comparison with subsequent load voltage values, percentage means for fixing the percentage of voltage change efiective to actuate said apparatus, and power means effective on change of comparator voltage to the set percentag value to operate said apparatus, said percentage means comprising a linear potential divider, an electrical bridge connected to the iivider normally underbalanced to prevent load :ontrol actuation, but becomin overbalanced to ause said apparatus actuation on development F a voltage change in said comparator.

3. In a system of power supply control including a power source and a, load unit receiving power from said source and subject to voltage change, load controlled circuital apparatus comprising a comparator connected to the load for fixing a component of the load voltage prior to voltage change for comparison with subsequent load voltage values, percentage means for fixing the percentage of voltage change effective to actuate said apparatus, and power means effective on change of comparator voltage to the set percentage value to operate said apparatus, said percentage means comprising a linear potential divider, an electrical bridge connected to the divider normally underbalanced to prevent load control actuation, but becoming overbalanced to cause said apparatus actuation on development of a voltage change in said comparator, and means for determination of the setting of the potential divider and the underbalance of said bridge.

4. In an electrical system including a power source and load, percentage control apparatus functioning on load voltage change comprising a voltage divider having linear change characteristics, a bridge circuit connected to said divider, and power means actuated by said bridge circuit, said bridge circuit comprising two parallelly connected units of a resistor and an electronic vacuum tube having a control grid connected in series, a source of power connected to the junction points between the resistors and between the tubes, power actuating means connected to the junction points between each resistor and tube, and means connected to the control grid of one of said tubes for maintaining a component of load voltage value existing prior to voltage change, the control grid of the other tube having connection to the load circuit and variable therewith.

5. In an electrical circuit subject to voltage change, apparatus for establishing the initial voltage existing prior to voltage change, and utilizing the change from this initial voltage to operate power means, comprising a bridge having two electronic tubes and two resistors connected in series with in-power connections between each resistor and between each. tube and out-power connections between each tube and resistor, an element connected to the grid of one of said tubes for fixing the prechange current voltage, and a connection between the control grid of the other tube and said circuit, whereby prior to circuit voltage change the bridge is unbalanced on a given bridge polarity, but on'circuit voltage change is unbalanced on a reversed bridge polarity to actuate said power means.

6. In an electrical circuit subject to voltage change, apparatus for establishing the initial voltage existing prior to voltage change, and utilizing the change from this initial voltage to oper-' ate power means, comprising a bridge having two electronic tubes and two resistors connected in series with input power connections between each resistor and between each tube and output powe connections between each tube and resistor, an element connected to the grid of one of said tubes for fixing the prechange current voltage, and a connection between the control grid of the other tube and said circuit, whereby prior to circuit voltage change the bridge is unbalanced on a given bridge polarity, but on cir-' cuit voltage change is unbalanced on a reversed bridge polarity to actuate said power means, and means for unbalancing said bridge prior to said voltage change.

7. In a system of power supply control includ-' ing "a power source and a load unit receiving power from said source and subject to voltage change, load controlled circuital apparatus oomprislng a compensator for correcting for current change in said source power, a comparator connected to the load for fixing a component of the load voltage prior to voltage change for comparison with subsequent load voltage values, percentage means for fixing the percentage of voltage change effective to actuate said apparatus, and power means efiective on change of comparator voltage to the'set percentage value to operate said apparatus.

-. 8. In a system including a variable alternating current power supply and a load, a circuit for delivering a rectified and compensated voltage component of said load, comprising means for rectifying a component of the load voltage, means for rectifying-a component of the load current, means for balancing said variable current cornponent with a fixed opposed voltage element,

a grid controlled electronic tube having an effective resistance dependent on the differential voltage of the variable current component and fixed voltage, and means for connecting said tube to said rectified load voltage component circuit to increase the effective resistance of said circuit on load current drop and to decrease the efiective resistance on load current increase whereby compensation of current change in said load circuit is secured in the rectified load voltage component circuit.

" 9. In a system of power supply control, a power source, a load unit receiving power from said source and subject to voltage change; and load .i.)

controlled means connected to the load unitior changing the magnitude of power supply, said load control means comprising a translating circuit connected to the load unit for amplifying and rectifying current voltage at said load, a comparator device for fixing a maximum mechange voltage component as applied to' said load and comparing this voltage with the load voltage component on load voltage change, and

bridge means balanced for cut-ofi prior to load voltage change andbalanced for power supply after load voltage change.

10. In a system of power supply control including a power source and a load unit receiving power from said source and subject to voltage change, means for rectifying and filtering the voltage across the load, load controlled ,circuital apparatus comprising a compensator for corre'cting for current change in said source power,

a comparator connected to the load for fixing a.

component of the load voltage prior to voltage change for comparison with subsequent load voltage values," means for reducing the filter charge lag, percentage means for fixing the percentage of voltage change effective to actuate said apparatus, and power means eflective on change of comparator voltage to the said percentage values to operate said apparatus.

11. In a system of power supply control, in combination, a power supply source, a load unit receiving power from said source in separate periods, the load unit being subject to dififerent resistance and voltage conditions for different periods and also subject to relatively sudden voltage change during each period, signal means responsive to the voltage across the load, means for compensating the load voltage signal for fluctuating current conditions, means for fixing for each period a proportional charge which is determined by the load voltage before change,

means for selectively varying the proportion oi said charge, and electrical comparator means responsive conjointly to said fixed proportional charge and to a charge which is determined by the load voltage after change for furnishing a control impulse.

12. In a system .of power supply control, in.

combination, a power supply source, a load unit receiving power from said source in separate periods, the load unit being subject to difierent resistance and voltage conditions for different periods and also subject to a relatively sudden voltage change during each period, signal means responsive to the voltage across the load, means for fixing for each period a proportional charge but balanced after voltage change.

13. In a system of power supply control, in combination, a power supply source, a load unit receiving power from said source in separate periods, the load unit being subject to different resistance and voltage conditions for different periods and also subject to a relatively sudden voltage change during each period, signal means responsive to the voltage across the load, means for fixing for each period a proportional charge which is determined proportionally according to an extreme value of the voltage before change, and electronic comparator means responsive conjointly to said fixed proportional charge and to a charge which is deter-mined by the load voltage after change for furnishing a control impulse, said electronic comparator means including paired vacuum grid tubes and a gas grid tube, the vacuum tubes respectively influencing the gas tube according to proportional and full voltage conditions at the load and causing it to fire at a predetermined comparative condtion for prechange and post-change load voltage conditions.

it. In a system for power supply control, in combination, a power supply source, a load unit receiving power from said source and being subject to voltage variation across the load, signal means responsive to voltage across the load, said signal means including conductors which are sub= ject .to voltage distortion at the load, means for compensating for said voltage distortion, means for fixing a proportional charge which is determined by corrected load signal voltage before voltage change, and comparator means respon= sive conjointly to said proportional charge before voltage change and to a charge which is deter mined by the load voltage after change forfurnishing a control impulse.

15. In a system for power supply control, in

combination, a power supply source, a load unit receiving power from said source and being subject to voltage variation across the load, signal means responsive to voltage across the load, said signal means including conductors which are subject to voltage distortion at the load, means for compensating for said voltage distortion, means for fixing a proportional charge which is determined by corrected load signal voltage before voltage change, and comparator means responsive conjointly to said proportional charge before voltage change and to a charge which is determined by the load voltage after change for furnishing a control impulse, said compensating means including an induction coil in a voltage signal conductor.

16. In a system for power supply control, in combination, a power supply source, a load unit receiving power from said source and being subject to voltage variation across the load, signal means responsive to voltage across the load, said signal means including conductors which are subject to voltage distortion at the load, means for compensating for said voltage distortion, means for fixing a proportional charge which is determined by corrected load signal voltage before voltage change, and comparator means responsive conjointly to said proportional charge before voltage change and to a charge which is determined by the load voltage after change for furnishing a control impulse, said compensating means including a variable induction in the voltage si nal circuit.

17. In a system of power supply control, in combination, a power supply source, a load unit receiving power from said source in separate periods, the load unit being subject to diflerent resistance and voltage conditions for difl'erent periods and also subject to relatively sudden voltage change during each period, signal means responsive to the voltage across the load, means for compensating the load voltage signalfor changed current conditions, means for fixing for each period a reference charge which is determined by the load voltage before change, electrical comparator means responsive conjointly to said fixed charge and to a charge which is determined by the load voltage after change for furnishing a control impulse when said last-mentioned charge attains a predetermined ratio with respect to said firstmentioned charge, and means for adjusting the predetermined ratio at which said control impulse is furnished.

18. In a system of power supply control for a welder, in combination, a power supply source, a welding load unit receiving power from said source in separate periods, the load unit being subject to different resistance and voltage conditions for diflerent weld periods and also subject to relatively sudden voltage change during each weld period, signal means responsive to the voltage across the load, means for compensating the load voltage signal for changed current conditions, means for fixing for each period a reference charge which is determined by the load voltage before change, electrical comparator means responsive conjointly to said fixed charge and to a charge which is determined by the load voltage after change for furnishing a control impulse when said last-mentioned charge attains a predetermined ratio with respect to said first-mentioned charge, and means for adjusting the predetermined ratio at which said control impulse is furnished.

EDWIN M. CAILENDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

